Data quality report

Public domain data

These data have no specific confidentiality restrictions for users. However, users must acknowledge data sources as it is not ethical to publish data without proper attribution. Any publication or other output resulting from usage of the data should include an acknowledgment.

The recommended acknowledgment is

"This study uses data from the data source/organisation/programme, provided by the British Oceanographic Data Centre and funded by the funding body."

Sea-Bird SBE 19 and SBE 19plus SEACAT Profiler CTDs

The SBE 19 SEACAT Profiler is a self-contained, battery powered, pumped CTD system designed to measure conductivity, temperature, and pressure in marine or fresh water environments to depths of 10,500 meters. It was replaced by the SBE 19 plus model in 2001. An updated version of this instrument is the SBE 19 plus V2, which incorporates an electronics upgrade and additional features, with six differentially amplified A/D input channels, one RS-232 data input channel, and 64 MB FLASH memory.

The standard CTD unit comes with a plastic housing (rated to 600 m), although this can be replaced by titanium housing for depths up to 7000 m. It is typically used for CTD profiling although a conversion kit is available for mooring deployments. The CTD can also be attached to an SBE 36 CTD Deck Unit and Power/Data Interface Module (PDIM) for real-time operation on single-core armored cable up to 10,000 m.

The standard SBE 5M pump may be replaced by an SBE 5P (plastic housing) or 5T (titanium housing) pump for use with dissolved oxygen and/or other pumped sensors. Further details can be found in the manufacturer's SBE 19 plus V2 instrument specification or the SBE 19 and SBE 19 plus user guides.

Seapoint Chlorophyll Fluorometer

The Seapoint Chlorophyll Fluorometer (SCF) is a low power instrument for in situ measurements of chlorophyll a. The SCF uses modulated blue LED lamps and a blue excitation filter to excite chlorophyll a. The fluorescent light emitted by the chlorophyll a passes through a red emission filter and is detected by a silicon photodiode. The low level signal is then processed using synchronous demodulation circuitry which generates an output voltage proportional to chlorophyll a concentration. The SCF may be operated with or without a pump.

Sensor specifications, current at August 2006, are given in the table below. More information can be found at the manufacturer's web site .

Sensor Specifications

Power requirements

8 - 20 VDC, 15 mA avg., 27 mA pk.

Output

0 - 5.0 VDC

Output Time Constant

0.1 sec.

Power-up transient period

< 1 sec.

Excitation Wavelength

470 nm CWL, 30 nm FWHM

Emission Wavelength

685 nm CWL, 30 nm FWHM

Sensing Volume

340 mm 3

Minimum Detectable Level

0.02 µg l -1

Gain

Sensitivity, V µg -1 l -1

Range, µg l -1

Sensitivity/Range

30x 10x 3x 1x

1.0 0.33 0.1 0.033

5 15 50 150

WETLabs C-Star transmissometer

This instrument is designed to measure beam transmittance by submersion or with an optional flow tube for pumped applications. It can be used in profiles, moorings or as part of an underway system.

Two models are available, a 25 cm pathlength, which can be built in aluminum or co-polymer, and a 10 cm pathlength with a plastic housing. Both have an analog output, but a digital model is also available.

This instrument has been updated to provide a high resolution RS232 data output, while maintaining the same design and characteristics.

BODC Processing

Data were received by BODC in one ASCII format file that was subsequently split into 86 separate files, one for each CTD profile. The series were reformatted to the internal QXF format using BODC transfer function 340. Sample calibrations were applied to the conductivity data. The following table details the mapping of variables to BODC parameter codes.

Original parameter name

Original Units

Description

BODC Parameter Code

BODC Units

Comments

Pressure

Decibars

Pressure exerted by the water column

PRESPR01

Decibars

Temperature

°C

Temperature of the water column

TEMPST01

°C

Conductivity

mS cm -1

Electrical conductivity of the water column calibrated against independent measurements

Following transfer to QXF, the data were screened using BODC's in-house visualisation software, EDSERPLO. Any data considered as suspect were flagged 'M'. Flags from the originator marking suspect data were retained during transfer and flagged 'L'.

Originator's Data Processing

Sampling Strategy

A total of 86 CTD casts were performed on FRV Scotia cruise 1207S (10 August 2007 - 01 September 2007) around the North Sea and Shetland. The data were collected between 04:00 and 20:00 hours during the period 10 August 2007 - 30 August 2007.

Rosette bottles were fired in order to obtain independent salinity measurements. The sample data were used to derive calibrations for the conductivity profiles collected by the CTD.

Data Processing

The raw CTD data files were processed through the SeaBird Electronics SeaSoft data processing software following standard procedures. The originators used in-house interactive visual display editing software to edit out individual spikes in the primary temperature and conductivity channels. An ASCII file was generated for each CTD cast and all files from a cruise were concatenated into one ASCII file which was submitted to BODC.

Field Calibrations

Independent salinity samples, obtained from the CTD rosette and spread throughout the cruise, were used to calibrate the CTD conductivity data. Outlying points were discarded, and between 48 and 72 data points were used to derive the calibrations. The sample analyses yielded a straight line conductivity calibration of the form y = mx + c, where m = 1.001716 and c = -0.075157.

The uncalibrated data and calibrations were submitted to BODC, who applied the appropriate corrections.